OPTICS PART 1 - RAY OPTICS

                              RAY OPTICS   

SPHERICAL MIRRORS

 It is the part of a hollow sphere whose one side is reflecting and other is opaque (silvered) .

There are two types of spherical mirrors :

1. Concave Mirror - It is a part of hollow sphere whose outer part is silvered and inner part is 

    reflecting . ( converging mirror )

2. Convex Mirror - It is a part of hollow sphere whose inner part is silvered and outer part is 

    reflecting . ( diverging mirror)

                                             

FOCAL PLANE

It is the plane passing through principal focus and perpendicular to principal axis.

RELATION BETWEEN FOCAL LENGTH AND RADIUS OF CURVATURE FOR CONVEX MIRROR ( F = R/2 )

        

angle ABE = angle DBE [law of reflection]                 -   1

angle ABE = angle BCF [ corresponding angle ]          -   2

angle DBE = angle CBF [ opposite angles ]                 -    3

from 1,2 and 3

angle BCF = angle CBF

therefore, BF = CF

As aperture is small so B is very near to P

therefore  PF = CF 

So F is the centre of PC

therefore PF = PC/2

or F = R/2 

KEY POINT

If mirror is immersed in any liquid there is no change in its focal length.

APPLICATIONS OF SPHERICAL MIRRORS

( A)  CONVEX MIRROR

      1. It is used as driver' s mirror because itt produces erect and small image, so field of view is 

          increased .

         

  2. It is used as a reflector in street lights.

        

                       

( B)  CONCAVE MIRROR

    1. It is used in shaving.

    2. It is used in solar cookers.

    3. It is used in dish antennas. 

    4. It is used in reflecting type telescope.

Reflecting Type Telescope